The theory and phenomenology of perturbative QCD based jet quenching

TL;DR

The article surveys perturbative QCD-based jet quenching in dense QCD media, focusing on how high-pT jets lose energy via medium-induced radiation and elastic interactions in DIS and heavy-ion collisions. It contrasts four main formalisms—Higher Twist (in-medium DGLAP), AMY, GLV, and ASW—for radiative energy loss, detailing how each treats single- and multi-emission physics and medium structure. Central observables such as medium-modified fragmentation functions and nuclear modification factors are linked to transport parameters like $\hat{q}$, and the paper discusses how different medium models (HTL, Debye screening) feed into energy-loss predictions. A standardized comparison (the QGP brick) highlights how the formalisms relate through common inputs, and the work outlines open questions and future directions for jet quenching, including LHC-scale tests and Monte Carlo developments.

Abstract

The study of the structure of strongly interacting dense matter via hard jets is reviewed. High momentum partons produced in hard collisions produce a shower of gluons prior to undergoing the non-perturbative process of hadronization. In the presence of a dense medium this shower is modified due to scattering of the various partons off the constituents in the medium. The modified pattern of the final detected hadrons is then a probe of the structure of the medium as perceived by the jet. Starting from the factorization paradigm developed for the case of particle collisions, we review the basic underlying theory of medium induced gluon radiation based on perturbative Quantum Chromo Dynamics (pQCD) and current experimental results from Deep Inelastic Scattering on large nuclei and high energy heavy-ion collisions, emphasizing how these results constrain our understanding of energy loss. This review contains introductions to the theory of radiative energy loss, elastic energy loss, and the corresponding experimental observables and issues. We close with a discussion of important calculations and measurements that need to be carried out to complete the description of jet modification at high energies at future high energy colliders.

Figures (10)

• Figure 1: DIS on a nucleon leading to the formation of a quark jet which showers gluons in vacuum leading to the formation of a collimated jet of hadrons.
• Figure 2: DIS on a large nucleus. A quark in a nucleon on the front side is struck and then propagates through the nucleons behind the struck nucleon. In the process both the quark and the ensuing shower gluons scatter off the soft glue field inside the nucleons. This modifies the shower pattern.
• Figure 3: A single Coulomb (or Glauber) gluon interaction between a hard jet and a proton in the nucleus.
• Figure 4: DIS on a nucleon leading to the formation of a quark and a radiated gluon. Left panel represents the complete diagram whereas the right panel represents the hadronic tensor. The dangling photon lines do not represent photon propagators, but rather the scattering of the quark off a photon. The photon propagator is not contained in the hadronic tensor, see text for details.
• Figure 5: Left panel: DIS on a nucleus leading to the formation of a quark jet which which is constrained to propagate through the nucleus without radiating. Its only interactions are scatterings. Right panel: The dominant length enhancement arises from nested scattering diagrams, where the blobs represent individual nucleons, see text for details.